GB1091893A - Improvements in or relating to control systems for vapour generating installations - Google Patents

Abstract

1,091,893. Programmed control of temperature; fluid-pressure servomotor systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. and JOHN BROWN LAND BOILERS Ltd. Jan. 26, 1965 [Jan.28, 1964], No.3618/64. Headings G3N and G3P. In a vapour generating installation, comprising a plurality of independent groups of fuel burners, the rate of supply of fuel to the burners in use is controlled by a system responsive to a firing rate control signal which is selected as the lesser of a vapour pressure signal and a heat exchanger metal temperature signal, when the control signal is greater than a first preset value the number of burner groups is progressively increased and when lower than a second preset value the number of groups is progressively reduced. As shown, a radiant type steam boiler 1 having a vertically elongated furnace 3 is fired by four horizontal rows of burners 5A-5D and hot gases leave the furnace by a lateral pass 7 over a primary superheater 9 and a secondary superheater 11. Each burner row is supplied with air entrained fuel from a coal pulverizing mill 15A- 15D fed by a feeder 25A-25D. Associated with the fuel burners are oil fired pilot burners to which fuel is supplied through a valve 27. The pressure in a steam main is sensed by a transducer 31 and fed to a controller 33, having the set point varied from a controller 35, providing a pressure error signal, having proportional, integral and differential terms, to a signal detector 45 having a second error signal input, having proportional, integral and differential terms, from a controller 43 scanning by a relay device 41 a plurality of superheater thermocouples, determining the highest metal temperature and comparing it with a set point from the controller 35. A detector 45 determines which error signal corresponds to the lowest firing rate and supplies it to the setting inputs of speed regulators 55A- 55D controlling the motors driving the feeders 25A-25D and to the setting input of a controller unit 65 for the valve 27, feedback is derived from a pressure responsive transducer 67. The set point controller 35 varies the set points of controllers 33, 43 to follow a desired starting programme. The lowest firing rate signal is also fed to a device 101, comprising a plurality of logic elements, Figs. 3-8 (not shown), responsive to the actuation of a switch 93, which is normally open and closes when the firing rate signal is above 95% of its maximum value and of a switch 91 which is normally open and closed when the signal is below 55%. The device 101 determines whether the number of burner groups is appropriate to the load on the boiler and the starting up or closing down of oil and coal burner groups and pulverizing mills in sequence.